What I mean to say is this: any church that approves contraceptive sex and calla it godly, will eventually approve homosexual marriage and call it godly. It's not just a slippery slope: it's a logical four-lane highway.
You are SO correct in pointing to one of the beginnings of the four lane (or more) highway slope: Another one is the acceptance of divorce + remarriage for first the laity, then the clergy.
In fact, serial marriage has become so “normalized” among the clergy I have heard some speak deridingly of those who take their vow seriously as “still on his first marriage”—as though that were some sort of character flaw.